Biopolar electrosurgical instruments apply high radiofrequency (RF) electrical current to a surgical site to cut, ablate, or coagulate tissue. A particular application of these electrosurgical effects is to seal luminal structures, such as blood vessels or gastrointestinal sites, or tissue edges. A typical electrosurgical instrument takes the form of a pair of forceps, with electrodes positioned on both jaws of the forceps. In an electrosurgical procedure, the electrodes are placed in close proximity to each other as the jaws are closed on a target site such that the path of current between the two electrodes passes through tissue within the target site. The mechanical force exerted by the jaws and the electrical current combine to create the desired surgical effect.
By controlling the level of mechanical pressure applied by the jaws, the gap distance between electrodes, and the intensity, frequency, and duration of the electrosurgical energy applied to the tissue, a surgeon can coagulate, cauterize, or seal tissue toward a therapeutic end. A typical goal of controlling the delivery of electrosurgical energy, more particularly, is to apply no more and no less than the precise amount of energy required to create the desired effect within the targeted sealing site, while minimizing deleterious effects to tissue peripheral to the target site. As tissue absorbs energy, such as radiofrequency energy, its impedance of radiofrequency energy increases. This increase in impedance is generally considered to be a measure of the degree to which the tissue has been “processed” toward a therapeutic endpoint state. Embodiments of the presently disclosed systems and methods are directed toward using target tissue impedance as a feedback signal to appropriately control the level of energy applied to a targeted sealing site.